Spontaneous activity. What is spontaneous brain activity? Spontaneous activity of muscle fibers

Needle EMG includes the following main techniques:

• standard needle EMG;
• EMG of a single muscle fiber;
• macroEMG;
• scanning EMG.

Standard needle electromyography

Needle EMG is an invasive research method performed using a concentric needle electrode inserted into the muscle. Needle EMG makes it possible to assess the peripheral neuromotor apparatus: the morphofunctional organization of musculoskeletal motor units, the state muscle fibers(their spontaneous activity), and with dynamic observation - to evaluate the effectiveness of treatment, the dynamics of the pathological process and the prognosis of the disease.

INDICATIONS

Motor neuron diseases spinal cord(ALS, spinal amyotrophies, poliomyelitis and post-polio syndrome, syringomyelia, etc.), myelopathies, radiculopathies, various neuropathies (axonal and demyelinating), myopathies, inflammatory muscle diseases (polymyositis and dermatomyositis), central movement disorders, sphincter disorders and a number of other situations , when it is necessary to objectify the state of motor functions and the movement control system, to assess the involvement of various structures of the peripheral neuromotor apparatus in the process.

CONTRAINDICATIONS

There are practically no contraindications to needle EMG. A limitation is considered to be the unconscious state of the patient, when he cannot voluntarily tense a muscle. However, even in this case, it is possible to determine the presence or absence of an ongoing process in the muscles (by the presence or absence of spontaneous activity of muscle fibers). Needle EMG should be performed with caution in those muscles that have severe purulent wounds, non-healing ulcers and deep burn lesions.

DIAGNOSTIC VALUE

Standard needle EMG occupies a central place among electrophysiological research methods for various neuromuscular diseases and is crucial in the differential diagnosis of neurogenic and primary muscular diseases.

Using this method, the severity of denervation in the muscle innervated by the affected nerve, the degree of its recovery, and the effectiveness of reinnervation are determined.

Needle EMG has found its application not only in neurology, but also in rheumatology, endocrinology, sports and professional medicine, pediatrics, urology, gynecology, surgery and neurosurgery, ophthalmology, dentistry and maxillofacial surgery, orthopedics and a number of other medical fields.

PREPARATION FOR THE STUDY

There is no need for special preparation of the patient for the study. Needle EMG requires complete relaxation of the muscles being examined, so it is performed with the patient lying down. The patient is exposed to the muscles being examined, placed on his back (or stomach) on a comfortable soft couch with an adjustable headrest, informed about the upcoming examination and explained how he should tense and then relax the muscle.

METHODOLOGY

The study is carried out using a concentric needle electrode inserted into the motor point of the muscle (the permissible radius is no more than 1 cm for large muscles and 0.5 cm for small ones). The motor unit potentials (MU) are recorded. When choosing PDEs for analysis, it is necessary to follow certain rules for their selection.

Reusable needle electrodes are pre-sterilized in an autoclave or other sterilization methods. Disposable sterile needle electrodes are opened immediately before examining the muscle.

After inserting the electrode into a completely relaxed muscle and each time it is moved, monitor for the possible occurrence of spontaneous activity.

Registration of MUAPs is carried out with minimal voluntary muscle tension, which makes it possible to identify individual MUAPs. 20 different MUAPs are selected, observing a certain sequence of moving the electrode in the muscle.

When assessing the condition of the muscle, a quantitative analysis of the detected spontaneous activity is carried out, which is especially important when monitoring the patient’s condition over time, as well as when determining the effectiveness of therapy. The parameters of the recorded potentials of various units are analyzed.

INTERPRETATION OF RESULTS

MU is a structural and functional element of skeletal muscle. It is formed by a motor neuron located in the anterior horn of the gray matter of the spinal cord, its axon, which emerges in the form of a myelinated nerve fiber as part of the motor root, and a group of muscle fibers that, using a synapse, form contact with the numerous branches of this axon deprived of the myelin sheath - terminals (Fig. 8-8).

Each muscle fiber of a muscle has its own terminal, is part of only one motor unit and has its own synapse. Axons begin to branch intensively at the level of several centimeters to the muscle in order to provide innervation to each muscle fiber that is part of a given motor unit. The motor neuron generates a nerve impulse, which is transmitted along the axon, amplifies at the synapse and causes contraction of all muscle fibers belonging to this motor unit. The total bioelectric potential recorded during such a contraction of muscle fibers is called the motor unit potential.

Rice. 8-8. Schematic representation of DE.

Motor unit potentials

A judgment about the state of the motor units of human skeletal muscles is obtained based on an analysis of the parameters of the potentials they generate: duration, amplitude and shape. Each MU is formed as a result of the algebraic addition of the potentials of all muscle fibers that are part of the MU, which functions as a single whole.

As the excitation wave propagates through the muscle fibers towards the electrode, a three-phase potential appears on the monitor screen: the first deflection is positive, then there is a fast negative peak, and the potential ends with a third, again positive deflection. These phases can have different amplitudes, durations and areas, which depend on how the abductor surface of the electrode is located in relation to the central part of the recorded MU.

The parameters of the MU reflect the size of the MU, the number, relative position of muscle fibers and the density of their distribution in each specific MU.

Duration of motor unit potentials is normal

The main parameter of the PDE is its duration, or duration, measured as the time in milliseconds from the beginning of the signal deviation from the center line until its complete return to it (Fig. 8-9).

The duration of PDE in a healthy person depends on the muscle and age. With age, the duration of PDE increases. In order to create unified norm criteria for the study of the PDE, special tables of normal average duration values ​​have been developed for different muscles of people of different ages.

A fragment of such tables is given below (Table 8-5).

A measure of assessing the state of the MU in a muscle is the average duration of 20 different MUs recorded at different points of the muscle under study. The average value obtained during the study is compared with the corresponding indicator presented in the table, and the deviation from the norm is calculated (as a percentage). The average duration of PDE is considered normal if it falls within the limits of ±l2% of the value given in the table (abroad, the average duration of PDE is considered normal if it falls within the limits of ±20%).

Rice. 8-9. Measuring the duration of the MUAP.

Table 8-5. Average duration in the MUAP in the most frequently studied muscles of healthy people, ms

Duration of motor unit potentials in pathology

The main pattern of changes in the duration of the MUAP under pathological conditions is that it increases in neurogenic diseases and decreases in synaptic and primary muscular pathologies.

In order to more thoroughly assess the degree of change in MUAP in muscles with various lesions of the peripheral neuromotor apparatus, for each muscle, use a histogram of the distribution of MUAP by duration, since their average value may be within the limits of normal deviations in cases of obvious muscle pathology. Normally, the histogram has the form of a normal distribution, the maximum of which coincides with the average duration of the MUAP for a given muscle.

For any pathology of the peripheral neuromotor apparatus, the shape of the histogram changes significantly.

Electromyographic stages of the pathological process

Based on changes in the duration of the MUAP in diseases of the spinal cord motor neurons, when in relatively short term you can monitor all the changes occurring in the muscles; six EMG stages have been identified, reflecting the general patterns of MU restructuring during the denervation-reinnervation process (DRP), from the very beginning of the disease to the almost complete death of the muscle [Gecht B.M. et al., 1997].

In all neurogenic diseases, the death of more or less motor neurons or their axons occurs. The remaining motor neurons innervate “foreign” muscle fibers that are deprived of nervous control, thereby increasing their number in their motor units. On the EMG, this process is manifested by a gradual increase in the parameters of the potentials of such motor units. The entire cycle of changes in the histogram of the distribution of MUAPs by duration in neuronal diseases conventionally fits into five EMG stages (Fig. 8-10), reflecting the process of compensatory innervation in the muscles. This division, although conditional, helps to understand and trace all stages of the development of DRP in each specific muscle, since each stage reflects a certain phase of reinnervation and the degree of its severity. It is inappropriate to present stage VI in the form of a histogram, since it reflects the end point of the “reverse” process, that is, the process of decompensation and destruction of the MU muscle.

Rice. 8-10. Five stages of DRP in the deltoid muscle of a patient with ALS during long-term follow-up. N (norm) - 20 MU and a histogram of their distribution by duration in the deltoid muscle of a healthy person; I, II, IIIA, IIIB, IV, V - MUAPs and histograms of their distribution in the corresponding EMG stage. On the abscissa axis - the duration of the MUAP, on the ordinate axis - the number of MUAPs of a given duration. Solid lines are the normal limits, broken lines are the average duration of the normal MUAP, arrows indicate the average duration of the MUPD in a given muscle of the patient during different periods of the examination (sequentially from stages I to V). Scale: vertical 500 µV, horizontal 10 ms.

Among specialists in our country, these stages are widely used in the diagnosis of various neuromuscular diseases. They are included in the computer program of domestic electromyographs, which allows the automatic construction of histograms indicating the stage of the process.

A change in stage in one direction or another during re-examination of the patient shows what the future prospects for the development of DRP are.

Stage 1: the average duration of PDE is reduced by 13-20%. This stage reflects the very initial phase of the disease, when denervation has already begun, and the process of reinnervation is not yet manifested electromyographically. Some part of the denervated muscle fibers, deprived of impulse influence due to pathology of either the motor neuron or its axon, drops out of the composition of some motor units. The number of muscle fibers in such motor units decreases, which leads to a decrease in the duration of individual potentials.

In stage I, a number of potentials that are narrower than in a healthy muscle appear, which causes a slight decrease in the average duration.

The histogram of the MDE distribution begins to shift to the left, towards smaller values.

Stage 2: the average duration of PDE is reduced by 21% or more. With drp, this stage is noted extremely rarely and only in cases where, for some reason, reinnervation does not occur or is suppressed by some factor (for example, alcohol, radiation, etc.), and denervation, on the contrary, increases and massive death of muscle fibers in the DE. THIS leads to the fact that most or almost all MUAPs become shorter than normal in duration, and therefore the average duration continues to decrease.

The histogram of the MDE distribution shifts significantly towards smaller values. Stages I - II reflect changes in motor units caused by a decrease in the number of functioning muscle fibers in them.

Stage 3: the average duration of the MUAP is within ±20% of the norm for this muscle. This stage is characterized by the appearance of a certain number of potentials of increased duration, which are not normally detected.

The appearance of these MUs indicates the beginning of reinnervation, that is, denervated muscle fibers begin to be included in other MUs, and therefore the parameters of their potentials increase. PDEs of both reduced and normal duration and increased duration are simultaneously recorded in the muscle; the number of enlarged PDEs in the muscle varies from one to several. The average duration of PDE in the PI stage may be normal, but the appearance of the histogram differs from the norm. It does not have the form of a normal distribution, but is “flattened”, stretched and begins to shift to the right, towards larger values. It is proposed to divide the PI stage into two subgroups - III A and III B. They differ only in that at the IPA stage the average duration of PDE is reduced by 1-20%, and at the IPA stage it either completely coincides with the average value of the norm or is increased by 1 -20%. In stage III B, a slightly larger number of PDEs of increased duration are recorded than in stage III A. Practice has shown that such a division of the third stage into two subgroups is not particularly important. In fact, stage III simply means the appearance of the first EMG signs of reinnervation in the muscle.

Stage IV: the average duration of PDE is increased by 21-40%. This stage is characterized by an increase in the average duration of MUAPs due to the appearance, along with normal MUAPs, of a large number of potentials of increased duration. PDE of reduced duration at this stage is recorded extremely rarely. The histogram is shifted to the right, towards larger values; its shape is different and depends on the ratio of normal and increased duration MDEs.

Stage V: the average duration of PDE is increased by 41% or more. This stage is characterized by the presence of predominantly large and “giant” PDEs, and PDEs of normal duration are practically absent. The histogram is significantly shifted to the right, stretched and, as a rule, open. This stage reflects the maximum volume of reinnervation in the muscle, as well as its efficiency: the more giant MUADs, the more effective the reinnervation.

Stage VI: the average duration of PDE is within the normal range or reduced by more than 12%. This stage is characterized by the presence of PDEs changed in shape (potentials of collapsing MUs). Their parameters may formally be normal or reduced, but the shape of the PDE is changed: the potentials do not have sharp peaks, they are stretched, rounded, the rise time of the potentials is sharply increased. This stage is noted at the last stage of decompensation of the spinal cord, when most of the spinal cord motor neurons have already died and intensive death of the rest occurs. Decompensation of the process begins from the moment when the process of denervation increases, and the sources of innervation become fewer and fewer. On EMG, the stage of decompensation is characterized by the following signs: MUAP parameters begin to decrease, giant MUAPs gradually disappear, the intensity of the PF increases sharply, giant MUFs appear, which indicates the death of many nearby muscle fibers. These signs indicate that in this muscle the motor neurons have exhausted their ability to sprout as a result of functional inferiority and are no longer able to exercise full control over their fibers. As a result, the number of muscle fibers in the motor units is progressively reduced, the mechanisms of impulse conduction are disrupted, the potentials of such motor units are rounded, their amplitude decreases, and their duration decreases. It is not practical to construct a histogram at this stage of the process, since it, like the average duration of the MUAP, no longer reflects the true state of the muscle. The main symptom of stage VI is a change in the shape of all MUAPs.

EMG stages are used not only for neurogenic, but also for various primary muscular diseases to characterize the depth of muscle pathology. In this case, the EMG stage does not reflect the DRP, but the severity of the pathology and is called the “EMG stage of the pathological process.” In primary muscular dystrophies, sharply polyphasic MUAPs may appear with satellites that increase their duration, which significantly increases its average value, corresponding to EMG stage 3 or even IV of the pathological process.

Diagnostic significance of EMG stages.

For neuronal diseases in the same patient in different muscles VARIOUS EMG stages are often detected - from III to V. Stage 1 is detected very rarely - at the very beginning of the disease, and only in individual muscles.

In axonal and demyelinating diseases, stages III and IV are more often found, and stages 1 and 2 are less common. When a significant number of axons die in some of the most affected muscles, stage V is detected.

In primary muscle diseases, muscle fibers are lost from the MU due to some muscle pathology: a decrease in the diameter of muscle fibers, their splitting, fragmentation or other damage that reduces the number of muscle fibers in the MU or reduces the volume of the muscle. All this leads to a decrease (shortening) in the duration of the PDE. Therefore, in most primary muscular diseases and myasthenia, stages 1 and 11 are detected, in polymyositis - at first only stages 1 and 2, and during recovery - stages 3 and even IV.

Motor unit potential amplitude

Amplitude is auxiliary, but very important parameter when analyzing PDE. It is measured “from peak to peak,” that is, from the lowest point of a positive peak to the highest point of a negative peak. When registering MUAPs on the screen, their amplitude is determined automatically. Both the average and maximum amplitude of the MUAP detected in the muscle under study are determined.

The average values ​​of the MUAP amplitude in the proximal muscles of healthy people in most cases are 500-600 µV, in the distal muscles - 600-800 µV, while the maximum amplitude does not exceed 1500-1700 µV. These indicators are very arbitrary and can vary to some extent. In children 8-12 years old, the average amplitude of the MUAP, as a rule, is in the range of 300-400 μV, and the maximum does not exceed 800 μV; In older children, these figures are 500 and 1000 μV, respectively. In the facial muscles, the amplitude of the MUAP is much lower.

In athletes, an increased amplitude of the MUAP is recorded in trained muscles. Consequently, an increase in the average amplitude of the MU in the muscles of healthy individuals involved in sports cannot be considered a pathology, since it occurs as a result of the restructuring of the MU due to prolonged load on the muscles.

In all neurogenic diseases, the amplitude of the MUAP, as a rule, increases in accordance with the increase in duration: the longer the duration of the potential, the higher its amplitude (Fig. 8-11).

Rice. 8-11. The amplitude of MUAPs, varying in duration.

The most significant increase in MUAP amplitude is observed in neuronal diseases, such as spinal amyotrophy and the consequences of poliomyelitis.

It serves as an additional criterion for diagnosing the neurogenic nature of pathology in the muscles. An increase in the amplitude of the MU is caused by a restructuring of the MU in the muscle, an increase in the number of muscle fibers in the electrode lead area, synchronization of their activity, as well as an increase in the diameter of the muscle fibers.

An increase in both the average and maximum MUAP amplitude is sometimes observed in some primary muscular diseases, such as polymyositis, primary muscular dystrophy, dystrophic myotonia, etc.

Shape of motor unit potentials

The shape of the MU depends on the structure of the MU, the degree of synchronization of the potentials of its muscle fibers, the position of the electrode in relation to the muscle fibers of the analyzed MU and their innervation zones. The shape of the potential has no diagnostic value.

A - PDE of low amplitude and reduced duration, recorded with myopathy; B - PDE of normal amplitude and duration, noted in a healthy person; C - PDE of high amplitude and increased duration in polyneuropathy; D - giant PDE (does not fit on the screen), recorded in spinal amyotrophy (amplitude - 1 2 752 μV, duration - more than 35 ms). Resolution 200 µV/d, sweep 1 ms/d.

Rice. 8-12. Polyphasic (A - 5 intersections, 6 phases) and pseudopolyphase (5 - 2 intersections, 3 phases and 9 turns, 7 of them in the negative part of the potential) PDE.

In clinical practice, the form of PDE is analyzed in terms of the number of phases and/or turns in potential. Each positive-negative potential deviation that reaches the isoline and crosses it is called a phase, and each positive-negative potential deviation that does not reach the isoline is called a turn.

A polyphase potential is one that has five phases or more and crosses the center line at least four times(Fig. 8-12, A). There may potentially be additional tournae that do not cross the center line (Fig. 8-12, B). Turns come in both the negative and positive parts of the potential.

In the muscles of healthy people, the MDE, as a rule, is represented by three-phase potential oscillations (see Fig. 8-9), however, when recording the MDE in the area of ​​the end plate, it can have two phases, losing its initial positive part.

Normally, the number of polyphasic PDEs does not exceed 5-15%. An increase in the number of polyphase MUs is considered as a sign of a violation of the MU structure due to the presence of some pathological process. Polyphasic and pseudopolyphasic MUAPs are recorded both in neuronal and axonal, and in primary muscular diseases (Fig. 8-13).

Rice. 8-13. Severely polyphasic PDE (21 phases), recorded in a patient with progressive muscular dystrophy. Resolution 1 00 µV/d, sweep 2 ms/d. The amplitude of the PDE is 858 μV, duration is 1 9.9 ms.

Spontaneous activity

Under normal conditions, when the electrode is stationary in a relaxed muscle of a healthy person, no electrical activity occurs. With pathology, spontaneous activity of muscle fibers or motor units appears.

Spontaneous activity does not depend on the will of the patient; he cannot stop it or cause it arbitrarily.

Spontaneous activity of muscle fibers

Spontaneous activity of muscle fibers includes fibrillation potentials (PF) and positive sharp waves (PSW). PF and POV are recorded exclusively under pathological conditions when a concentric needle electrode is introduced into the muscle (Fig. 8-14). PF is the potential of one muscle fiber, POV is a slow oscillation that follows a rapid positive deflection and does not have an acute negative peak. The SOM reflects the participation of both one and several adjacent fibers.

Rice. 8-14. Spontaneous activity of muscle fibers. A - fibrillation potentials; B - positive sharp waves.

The study of spontaneous activity of muscle fibers in a clinical study of a patient is the most convenient electrophysiological method that allows us to judge the degree of usefulness and stability of nerve influences on muscle fibers of skeletal muscle in its pathology.

Spontaneous activity of muscle fibers can occur with any pathology of the peripheral neuromotor apparatus. In neurogenic diseases, as well as in synapse pathology (my asthenia and myasthenic syndromes), the spontaneous activity of muscle fibers reflects the process of their denervation. In most primary muscle diseases, the spontaneous activity of muscle fibers reflects any damage to the muscle fibers (their splitting, fragmentation, etc.), as well as their pathology caused by the inflammatory process (in inflammatory myopathies - polymyositis, dermatomyositis).

In both cases, PF and POV indicate the presence of an ongoing process in the muscle; Normally they are never registered.

The duration of the PF is 1-5 ms (it does not have any diagnostic value), and the amplitude fluctuates within a very wide range (on average 118 ± 1 14 μV). Sometimes high-amplitude (up to 2000 μV) PFs are also detected, usually in patients with chronic diseases. The timing of the onset of PF depends on the location of the nerve lesion. In most cases, they occur 7-20 days after denervation.

If for some reason reinnervation of the denervated muscle fiber does not occur, it dies over time, generating waveforms that consider EMG to be a sign of the death of a denervated muscle fiber that has not received the innervation it previously lost. By the number of PF and SOM recorded in each muscle, one can indirectly judge the degree and depth of its denervation or the volume of dead muscle fibers. The duration of the POV ranges from 1.5 to 70 ms (in most cases up to 10 ms). So-called giant SEFs lasting more than 20 ms are detected with prolonged denervation of a large number of adjacent muscle fibers, as well as with polymyositis. The amplitude of the SOV varies, as a rule, from 10 to 1800 μV. SOVs of large amplitude and duration are more often detected in later stages of denervation ("giant" SOVs). PEFs begin to be recorded 1–6–30 days after the first appearance of PF; they can persist in the muscle for several years after denervation.

As a rule, in patients with inflammatory lesions of peripheral nerves, POV is detected later than in patients with traumatic lesions. PF and POV respond most quickly to the start of therapy: if it is effective, the severity of PF and POV decreases after 2 weeks. On the contrary, when treatment is ineffective or insufficiently effective, their severity increases, which makes it possible to use the analysis of PF and SPV as an indicator of the effectiveness of the drugs used.

Myotonic and pseudomyotonic discharges

Myotonic and pseudomyotonic discharges, or high frequency discharges, also refer to the spontaneous activity of muscle fibers. Myotonic and pseudomyotonic discharges are distinguished by a number of features, the main of which is the high repeatability of the elements that make up the discharge, that is, the high frequency of potentials in the discharge. The term "pseudomyotonic discharge" is increasingly being replaced by the term "high frequency discharge".

Myotonic discharges are a phenomenon detected in patients with various forms of myotonia. When listened to, it resembles the sound of a "dive bomber". On the monitor screen, these discharges appear as repeating potentials of gradually decreasing amplitude, with progressively increasing intervals (which causes a decrease in the pitch of the sound, Fig. 8-15). Myotonic discharges are sometimes observed in some forms of endocrine pathology (for example, hypothyroidism). Myotonic discharges occur either spontaneously or after a slight contraction or mechanical stimulation of the muscle with a needle electrode inserted into it or simple tapping on the muscle.

Pseudomyotonic discharges (high frequency discharges) are recorded in some neuromuscular diseases, both associated and not associated with denervation of muscle fibers (Fig. 8-16). They are considered a consequence of the ephaptic transmission of excitation with a decrease in the insulating properties of the muscle fiber membrane, which creates the precondition for the spread of excitation from one fiber to the adjacent one: the pacemaker of one of the fibers sets the rhythm of impulses, which is imposed on the adjacent fibers, which determines the peculiar shape of the complexes. Discharges start and stop suddenly. Their main difference from myotonic discharges is the absence of a drop in the amplitude of the components. Pseudomyotonic discharges are observed in various forms of myopathy, polymyositis, denervation syndromes (in the late stages of reinnervation), spinal and neural amyotrophies (Charcot-Marie-Tooth disease), endocrine pathology, trauma or nerve compression and some other diseases.

Rice. 8-15. Myotonic discharge recorded in the tibialis anterior muscle of a patient (1–9 years old) with Thomsen's myotonia. Resolution 200 µV/d.

Rice. 8-16. A high-frequency discharge (pseudomyotonic discharge) recorded in the tibialis anterior muscle of a patient (32 years old) with neural amyotrophy (Charcot-Marie-Tooth disease) type IA. The discharge stops suddenly, without a preliminary drop in the amplitude of its components. Resolution 200 µV/d.

Spontaneous motor unit activity

Spontaneous activity of motor units is represented by fasciculation potentials. Fasciculations are spontaneous contractions of the entire motor unit that occur in a completely relaxed muscle. Their occurrence is associated with diseases of the motor neuron, its overload with muscle fibers, irritation of any of its areas, and functional and morphological changes (Fig. 8-17).

The appearance of multiple fasciculation potentials in muscles is considered one of the main signs of damage to spinal cord motor neurons.

The exception is “benign” fasciculation potentials, sometimes detected in patients who complain of constant twitching in the muscles, but do not notice muscle weakness and other symptoms. Single fasciculation potentials can also be detected in neurogenic and even primary muscular diseases, such as myotonia, polymyositis, endocrine, metabolic and mitochondrial myopathies.

Rice. 8-17. Fasciculation potential against the background of complete relaxation of the deltoid muscle in a patient with the bulbar form of ALS. The amplitude of the fasciculation potential is 1,580 μV. Resolution 200 µV/d, sweep 10 ms/d.

Fasciculation potentials that occur in athletes are described highly qualified after an exhausting physical activity. They can also occur in healthy but easily excitable people, in patients with carpal tunnel syndromes, polyneuropathies, and in the elderly. However, unlike motor neuron diseases, their number in the muscle is very small, and the parameters are usually normal.

The parameters of fasciculation potentials (amplitude and duration) correspond to the parameters of the MUAP recorded in a given muscle and can change in parallel with changes in the MUAP during the development of the disease.

Needle electromyography in the diagnosis of diseases of motor neurons of the spinal cord and peripheral nerves

In any neurogenic pathology, DRP occurs, the severity of which depends on the degree of damage to the sources of innervation and on what level of the peripheral neuromotor apparatus - neuronal or axonal - the damage occurred. In both cases, the lost function is restored due to the preserved nerve fibers, and the latter begin to branch intensively, forming numerous sprouts heading to the denervated muscle fibers. This branching received the name “sprouting” in the literature (English “sprout” - to sprout, branch).

There are two main types of sprouting - collateral and terminal.

Collateral sprouting is the branching of axons in the area of ​​nodes of Ranvier, terminal sprouting is the branching of the final, unmyelinated section of the axon.

It has been shown that the nature of sprouting depends on the nature of the factor that caused the disturbance of nervous control. For example, during botulinum intoxication, branching occurs exclusively in the terminal zone, and during surgical denervation, both terminal and collateral sprouting occurs.

On the EMG, these states of motor units at various stages of the reinnervation process are characterized by the appearance of motor units of increased amplitude and duration.

The exception is the very initial stages of the bulbar form of ALS, in which the parameters of the MUAP are within the limits of normal variations for several months.

EMG criteria for spinal cord motor neuron diseases

The presence of pronounced fasciculation potentials (the main criterion for damage to spinal cord motor neurons).

An increase in the parameters of the MUAP and their polyphasia, reflecting the severity of the reinnervation process.

The appearance in the muscles of spontaneous activity of muscle fibers - PF and PAV, indicating the presence of an ongoing denervation process.

Fasciculation potentials are a mandatory electrophysiological sign of damage to spinal cord motor neurons. They are detected already in the very early stages of the pathological process, even before signs of denervation appear.

Due to the fact that neuronal diseases imply a constant ongoing process of denervation and reinnervation, when a large number of motor neurons simultaneously die and a corresponding number of MUs are destroyed, MUDEs become increasingly larger, their duration and amplitude increase. The degree of increase depends on the duration and stage of the disease.

The severity of PF and POV depends on the severity of the pathological process and the degree of muscle denervation. In rapidly progressing diseases (for example, ALS), PF and POV are found in most muscles, in slowly progressing diseases (some forms of spinal amyotrophy) - only in half of the muscles, and in post-polio syndrome - in less than a third. EMG criteria for peripheral nerve axonal diseases

Needle EMG in the diagnosis of diseases of peripheral nerves is an additional but necessary examination method that determines the degree of damage to the muscle innervated by the affected nerve. The study makes it possible to clarify the presence of signs of denervation (DF), the degree of loss of muscle fibers in the muscle (the total number of DEFs and the presence of giant DEFs), the severity of reinnervation and its effectiveness (the degree of increase in DEF parameters, maximum value amplitude of the MUAP in the muscle). The main emg signs of the axonal process:

• increase in the average amplitude of the MUAP;
• presence of PF and POV (with current denervation);
• an increase in the duration of the MUAP (the average value may be within the normal range, that is, ±12%);
• PDE polyphasia;
• single fasciculation potentials (not in every muscle).

When axons of peripheral nerves are damaged (various polyneuropathies), DRP also occurs, but its severity is much less than in neuronal diseases. Consequently, MDEs are increased to a much lesser extent. Nevertheless, the basic rule of changes in the MUAP in neurogenic diseases also applies to damage to the axons of motor nerves (that is, the degree of increase in MUAP parameters and their polyphasia depend on the degree of nerve damage and the severity of reinnervation). The exception is pathological conditions accompanied by rapid death of motor nerve axons due to injury (or some other pathological condition leading to the death of a large number of axons). In this case, the same giant MUAPs appear (with an amplitude of more than 5000 μV) as in neuronal diseases. Such PDEs are observed in long-term forms of axonal pathology, CIDP, and neural amyotrophies.

If, with axonal polyneuropathies, the amplitude of the MUAP increases first of all, then during the demyelinating process, with a deterioration in the functional state of the muscle (a decrease in its strength), the average duration of the MUAP gradually increases; much more often than in the axonal process, polyphasic MUAPs and fasciculation potentials are detected, and less often - PF and PV.

Needle electromyography in the diagnosis of synaptic and primary muscle diseases

For synaptic and primary muscle diseases, a decrease in the average duration of the MUAP is typical. The degree of decrease in MUAP duration correlates with the decrease in strength. In some cases, the PDE parameters are within the limits of normal deviations, and with PMD they can even be increased (see Fig. 8-13).

Needle electromyography for synaptic diseases

In synaptic diseases, needle EMG is considered additional method research. In myasthenia gravis, it allows one to assess the degree of “blocking” of muscle fibers in the MU, determined by the degree of decrease in the average duration of the MU in the examined muscles. Nevertheless, the main purpose of needle EMG for myasthenia gravis is to exclude possible concomitant pathology (polymyositis, myopathy, endocrine disorders, various polyneuropathies, etc.). Needle EMG in patients with myasthenia gravis is also used to determine the degree of response to the administration of anticholinesterase drugs, that is, to assess changes in PDE parameters with the administration of neostigmine methyl sulfate (proserin). After administration of the drug, the duration of PDE in most cases increases. Lack of response may indicate so-called myasthenic myopathy.

Basic EMG criteria for synaptic diseases:

• decrease in the average duration of PDE;
• decrease in the amplitude of individual MUAPs (may be absent);
• moderate polyphasia of the PDE (may be absent);
• absence of spontaneous activity or presence of only single PFs.

With myasthenia gravis, the average duration of PDE is, as a rule, slightly reduced (by 10-35%). The predominant number of MUAPs has a normal amplitude, but several MUAPs of reduced amplitude and duration are recorded in each muscle. The number of polyphasic PDEs does not exceed 15-20%. There is no spontaneous activity. If pronounced PF is detected in a patient, one should think about a combination of myasthenia gravis with hypothyroidism, polymyositis or other diseases.

Needle electromyography for primary muscular diseases

Needle EMG is the main electrophysiological method for diagnosing primary muscle diseases (various myopathies). Due to a decrease in the ability of motor units to develop sufficient force to maintain even minimal effort, a patient with any primary muscular pathology has to recruit a large number of motor units. This determines the peculiarity of EMG in such patients. With minimal voluntary muscle tension, it is difficult to identify individual MUAPs; so many small potentials appear on the screen that this makes their identification impossible. This is the so-called myopathic EMG pattern (Fig. 8-18).

In inflammatory myopathies (polymyositis), a process of reinnervation takes place, which can cause an increase in PDE parameters.

Rice. 8-18. Myopathic pattern: measuring the duration of individual MUs is extremely difficult due to the recruitment of a large number of small MUs. Resolution 200 µV/d, sweep 10 ms/d.

Basic EMG criteria for primary muscle diseases:

• a decrease in the average duration of PDE by more than 1–2%;
• decrease in the amplitude of individual MUAPs (the average amplitude can be either reduced or normal, and sometimes increased);
• PDE polyphasia;
• pronounced spontaneous activity of muscle fibers in inflammatory myopathy (polymyositis) or PMD (in other cases it is minimal or absent).

A decrease in the average duration of the MUAP is a cardinal sign of any primary muscle disease. The reason for this change is that with myopathies, muscle fibers undergo atrophy, some of them fall out of the MU composition due to necrosis, which leads to a decrease in MU parameters.

A decrease in the duration of most MUAPs is detected in almost all muscles of patients with myopathies, although it is more pronounced in the clinically most affected proximal muscles.

The histogram of the distribution of PDE by duration shifts towards smaller values ​​(stage 1 or 11). An exception is PMD: due to the sharp polyphasia of PDE, sometimes reaching 100%, the average duration can be significantly increased.

Single muscle fiber electromyography

EMG of a single muscle fiber allows you to study the electrical activity of individual muscle fibers, including determining their density in the muscle motor units and the reliability of neuromuscular transmission using the jitter method.

To carry out the study, a special electrode with a very small tapping surface with a diameter of 25 microns, located on its side surface 3 mm from the end, is required. The small abductor surface allows recording the potentials of a single muscle fiber in a zone with a radius of 300 µm.

Muscle fiber density test

The basis for determining the density of muscle fibers in D E is the fact that the microelectrode abduction zone for recording the activity of a single muscle fiber is strictly defined. A measure of the density of muscle fibers in the MU is the average number of potentials of single muscle fibers recorded in the zone of its abduction when studying 20 different MUs in different muscle zones. Normally, this zone can contain only one (less often two) muscle fiber belonging to the same motor unit. Using a special methodological technique (trigger device), it is possible to avoid the appearance on the screen of potentials of single muscle fibers belonging to other motor units.

The average fiber density is measured in arbitrary units by calculating the average number of potentials of single muscle fibers belonging to different motor units. In healthy people, this value varies depending on the muscle and age from 1.2 to 1.8. An increase in the density of muscle fibers in the MU reflects a change in the structure of the MU in the muscle.

Study of the Jitter Phenomenon

Normally, it is always possible to position the electrode for recording a single muscle fiber in a muscle so that the potentials of two adjacent muscle fibers belonging to the same motor unit are recorded. If the potential of the first fiber triggers the trigger device, then the potential of the second fiber will be slightly different in time, since for the impulse to pass through two nerve terminals different lengths required different times. This is reflected in the variability of the inter-peak interval, that is, the registration time of the second potential fluctuates in relation to the first, defined as the “dance” of the potential, or “jitter”, the value of which is normally 5-50 μs. Jitter reflects the variability in the timing of neuromuscular transmission at the two motor end plates, so this method allows us to study a measure of the stability of neuromuscular transmission. When it is disrupted, caused by any pathology, jitter increases. Its most pronounced increase is observed in synaptic diseases, primarily in myasthenia gravis (Fig. 8-19).

With a significant deterioration in neuromuscular transmission, a condition occurs when the nerve impulse cannot excite one of the two adjacent fibers and the so-called impulse blocking occurs (Fig. 8-20).

A significant increase in jitter and instability of individual PDE components is also observed in ALS. This is explained by the fact that newly formed terminals and immature synapses as a result of sprouting operate with an insufficient degree of reliability. At the same time, in patients with rapid progression of the process, the most pronounced jitter and blocking of pulses are observed.

Rice. 8-19. An increase in jitter (490 μs when the norm is less than 50 μs) in the common extensor digitorum in a patient with myasthenia gravis (generalized form).

Superposition of 10 sequentially repeating complexes of two potentials of one motor unit. The first potential is the trigger potential. Resolution 0.2 m V/d, sweep 1 ms/d.

Rice. 8-20. Increased jitter (260 µs) and impulse blocking (on the 2nd, 4th and 9th lines) in the common extensor digitorum of the same patient (see Fig. 8-19). The first impulse is the trigger.

Macroelectromyography

Macro-EMG allows one to judge the size of motor units in skeletal muscles. During the study, two needle electrodes are used simultaneously: a special macroelectrode inserted deep into the muscle so that the abducting side surface of the electrode is located deep in the muscle, and a conventional concentric electrode inserted under the skin. The macro-EMG method is based on the study of the potential recorded by a macroelectrode with a large abductor surface.

A conventional concentric electrode serves as a reference electrode, inserted under the skin at a distance of at least 30 cm from the main macroelectrode into the zone of minimal activity of the muscle being studied, that is, as far as possible from the motor point of the muscle.

Another electrode mounted in the cannula for recording the potentials of single muscle fibers registers the potential of the muscle fiber of the studied motor unit, which serves as a trigger for averaging the macropotential. The signal from the cannula of the main electrode also enters the averager. 130-200 pulses are averaged (an epoch of 80 ms; a period of 60 ms is used for analysis) until a stable isoline and a macropotential MU that is stable in amplitude appear. Registration is carried out on two channels: on one, the signal from one muscle fiber of the studied motor unit is recorded, which triggers averaging; on the other, the signal between the main and reference electrodes is reproduced.

The main parameter used to assess the macropotential of a motor unit is its amplitude, measured from peak to peak. The duration of the potential does not matter when using this method. It is possible to estimate the area of ​​macropotentials DE. Normally, there is a wide range of amplitude values; with age, it increases slightly. In neurogenic diseases, the amplitude of MU macropotentials increases depending on the degree of reinnervation in the muscle. In neuronal diseases it is highest.

In the later stages of the disease, the amplitude of MU macropotentials decreases, especially with a significant decrease in muscle strength, which coincides with a decrease in MU parameters recorded with standard needle EMG.

In myopathies, a decrease in the amplitude of macropotentials of motor units is noted, however, in some patients their average values ​​are normal, but nevertheless they still note a certain number of potentials of reduced amplitude. None of the studies examining the muscles of patients with myopathy revealed an increase in the average amplitude of MU macropotentials.

The macro-EMG method is very labor-intensive, so it is not widely used in routine practice.

Scanning electromyography

The method allows you to study the temporal and spatial distribution of electrical activity of the MU by scanning, that is, stepwise movement of the electrode in the area where the fibers of the MU under study are located. Scanning EMG provides information about the spatial location of muscle fibers throughout the entire MU space and can indirectly indicate the presence of muscle groups that are formed as a result of the process of denervation of muscle fibers and their repeated reinnervation.

With minimal voluntary muscle tension, an electrode inserted into it to record a single muscle fiber is used as a trigger, and with the help of a concentric needle (scanning) electrode, the PDE is recorded from all sides with a diameter of 50 mm. The method is based on slow, step-by-step immersion of a standard needle electrode into the muscle, accumulation of information about changes in the potential parameters of a certain motor unit and construction of the corresponding image on the monitor screen. Scanning EMG is a series of oscillograms located one below the other, each of which reflects fluctuations in the biopotential recorded at a given point and captured by the abducting surface of a concentric needle electrode.

Subsequent computer analysis of all these MUAPs and analysis of their three-dimensional distribution gives an idea of ​​the electrophysiological profile of motoneurons.

When analyzing scanning EMG data, the number of main peaks of the MU, their shift in time of appearance, the duration of the intervals between the appearance of individual fractions of the potential of a given MU are assessed, and the diameter of the fiber distribution zone in each of the examined MUs is calculated.

With DRP, the amplitude and duration, as well as the area of ​​potential oscillations on the scanning EMG increase. However, the diameter of the fiber distribution zone of individual MUs does not change significantly. The number of fractions characteristic of a given muscle does not change either.

This suggests that a neuroactive substance may be produced as a result of TEPP treatment.

In cockroaches and crayfish whose DDT poisoning has progressed so far that it is irreversible, the spontaneous activity of the central nervous system is depressed or almost absent. If the nerve chain of such cockroaches is carefully dissected and washed in physiological solution, then a higher level of spontaneous activity returns to it. In this case, washing removes some

Isoclins of the system with parameters corresponding to the axon membrane are shown in Fig. ХХШ.27. The singular point is stable (located on the left branch), and the membrane does not exhibit spontaneous activity. The resting potential level is conventionally taken to be zero. When the parameters change, the isoclines become deformed. If in this case the singular point becomes unstable (shifts from the left branch of the isocline d(f/dt = O to the middle one), then spontaneous activity will arise (Fig. XXX.28,1). If

I - spontaneous activity (singular point 8 is unstable, lies on the middle branch); the dotted line shows the projection of the limit cycle of the system onto the plane

It is very interesting that even after the victory of the myogenic theory, the idea of ​​spontaneous activity was alien to many biologists for a long time. They said that every reaction must be a response to some kind of influence, like a reflex. In their opinion, admitting that muscle cells can contract on their own is the same as abandoning the principle of causality. They were ready to explain the contraction of heart cells by anything, but not by their own properties (for example, special fantastic hormones or even the action of cosmic rays). Our generation still sees heated discussions on this issue.

It was shown above how nerve cells conduct, process and record electrical signals, and then send them to the muscles to cause their Contraction. But where do these signals come from? There are two spontaneous excitation and sensory stimuli. There are spontaneously active neurons, for example neurons of the brain that set the rhythm of breathing. A very complex pattern of spontaneous activity can be generated in a single cell using the appropriate combinations of ion channels of the types that we have already encountered when discussing the mechanisms of information processing by neurons. The reception of sensory information is also based on principles already known to us, but it involves cells of very diverse and surprising types.

Individuals with monomorphic a-waves, on average, show themselves to be active, stable and reliable people. Probands are highly likely to show signs of high spontaneous activity and perseverance; accuracy in work, especially under stress, and short-term memory are their strongest qualities. On the other hand, they do not process information very quickly.

Toxic concentrations. For animals. Mice. With a two-hour exposure, the minimum concentrations causing lateral position are 30-35 mg/l, anesthesia - 35 mg/l, death - 50 mg/l (Lazarev). 17 mg/l causes a large decrease in the spontaneous activity of white mucous membranes (Goeppel et al.). Guinea pigs . 21 mg/l causes

A toxic substance accumulates in the hemolymph of the American cockroach Periplaneta ameri ana L, poisoned with DDT. Chemical analysis showed the absence of significant amounts of DDT in such hemolymph. Injection of DDT-sensitive and resistant cockroaches with hemolymph taken from cockroaches that were in the prostration phase as a result of DDT poisoning caused typical symptoms of DDT poisoning. Further, the same hemolymph led to an increase in the spontaneous activity of the nerve chain isolated from an unpoisoned cockroach. After a short period of strong arousal, activity suddenly dropped and blockage occurred. Since DDT itself does not have a direct effect on the central nervous system, it has been suggested that the above phenomena are caused by some other compound.

If the initial TEPP perfusate, which washed the nerve chain, is refilled with the latter, then spontaneous activity again increases greatly compared to normal, then gradually decreases to a low level, and in some cases blocking occurs. As before, rinsing with fresh 10 3 M TEPP solution returns the nerve to its original spontaneous activity.

From cockroaches. The neuroactive substance from the hemolymph of cockroaches that are in the prostration phase as a result of DDT poisoning was partially isolated by chromatography. After development of the chromatogram, the active substance was extracted from individual parts of the chromatograms by extraction with physiological solution, after which the effect of the extracts on the spontaneous activity of the cockroach nerve chain was determined. Using various solvents and repeatedly separating the neuroactive fractions by chromatography, we obtained a good separation of the neuroactive substance from various substances located in the hemolymph. Due to the loss of a substance or its biological activity during numerous chromatographic separation operations, as well as due to the difficulty of obtaining large quantities of cockroach hemolymph, attempts to select compounds for the qualitative recognition of this substance were carried out only with a limited set of compounds, and only one of them gave positive results. Treatment of chromatograms with diazotized p-nitroaniline led to the appearance of red-colored spots in the areas where biologically active substances of the hemolymph extract were localized. In chromatograms of extracts from the hemolymph of normal cockroaches, red spots did not appear in places corresponding to the Rj of the active substance.

The blood of crayfish poisoned with DDT was treated in the same way as the hemolymph of cockroaches, and it turned out to be neuroactive in experiments with the nervous circuit of the crayfish and the cockroach and first caused excitation, followed by depression of spontaneous activity. Only one difference was noted: the substance from the blood of the cancer was more active on the nerves of the cancer than on the nerves

Until now, the discussion has been based on the classical picture of the action of FOS, i.e. it was assumed that FOS affects the nervous system of insects by inhibiting cholinesterase, which in turn leads to dysfunction of acetylcholine. A study by Sternburg et al. questioned the value of this assumption. They took an isolated chain of an American cockroach and placed it in a saline solution and observed high spontaneous activity. This fluid was then replaced with 10 M TEPP in saline and, as expected, a rapid and complete block occurred. The mixture of TEPP with saline solution was temporarily removed; let's call this mixture t. After this, the preparation was washed several times with a freshly prepared mixture of TEPP with saline solution, as a result of which normal spontaneous activity was restored. If the drug was then treated again with mixture T, then excitation followed by blockade was observed.

The computer-calculated null isoclines are shown in Fig. XXIII.27. The isocline d(f/dt = O has an N-shape, which ensures the generation of an impulse. The singular point is located on the left branch of the isocline d(f/dt = O and is stable. This corresponds to the absence of spontaneous activity in the original Hodgkin-Huxley equations.

However, about a hundred years ago, the English physiologist Gaskell seriously criticized this theory and put forward a number of arguments in favor of the fact that the muscle cells themselves in some areas of the heart are capable of spontaneous rhythmic activity (myogenic theory). For over half a century, there was a fruitful scientific debate, which ultimately led to the victory of the myogenic theory. It turned out that in the heart there are actually two sections of special muscle tissue, the cells of which have spontaneous activity. One site is located in the right atrium (called the sinoatrial node), the other is on the border of the atrium and ventricle (the so-called atrioventricular node). The first has a more frequent rhythm and determines the work of the heart under normal conditions (then they say that the heart has sinus rhythm), the second is a backup if the first node stops, then after a while the second section begins to work and the heart begins to beat again, although at a slower rate rhythm. If you isolate individual muscle cells from one or another area and place them in a nutrient medium, then these cells continue to contract in their characteristic rhythm: sinus - more often, atrio-ventricular - less often.

We said that the retinal rods react to the stimulation of just one molecule of rhodopsin. But such excitation can occur not only under the influence of light, but also under the influence of thermal noise. As a result of the high sensitivity of the rods in the retina, false alarm signals should constantly occur. However, in reality, the retina also has a noise control system based on the same principle. The rods are interconnected by an ES, which leads to the averaging of shifts in their potential, so that everything happens in the same way as in electroreceptors (only there the signal is averaged in the fiber, which receives signals from many receptors, and in the retina - directly in the receptor system). And remember the unification of spontaneously active cells of the sinus node of the heart through highly permeable contacts, which gives a regular heart rhythm and eliminates the fluctuations inherent in a single cell (noise). We see that nature

Normally, no spontaneous activity is recorded in a relaxed muscle. In neurogenic diseases, two types of spontaneous activity of muscle fibers can be recorded - fibrillation potentials (PF) and positive sharp waves (PSW). PFs in neurogenic (and synaptic) diseases are potentials of denervated muscle fibers that have lost connection with axon terminals, but they can be reinnervated and become part of another motor unit. POV is an EMG sign of dead muscle fibers that, for some reason, could not receive innervation. The more PF registered in a muscle, the greater the degree of its denervation. The more SOM detected in a muscle, the more dead muscle fibers there are.

There is also no consensus in the literature regarding the detection of spontaneous activity of muscle fibers in patients with myasthenia gravis. Some authors mentioned the presence of PF and POV in patients with myasthenia gravis, others did not find them. In our study, PF and POM were detected in 33% of the examined muscles of patients with myasthenia gravis, but their number in the muscle was not large and ranged from 1 to 5 PF (average number 1.3 + 1.1). No spontaneous activity was detected in 67% of the muscles of patients in this group. It was also noted that PF are detected much more often in patients with myasthenia gravis in combination with thymoma.

POMs were detected in only 21% of muscles, and they were recorded in the same muscles in which PF were detected. Their severity in the muscle did not exceed 2 POV, the average value was only 0.4±0.7 POV. Single fasciculation potentials (SFPs) were detected in 13% of muscles.

The results obtained showed that in patients with myasthenia gravis, in a number of cases, denervation of individual muscle fibers occurs, manifested in the form of PF, while PFI, indicating the death of the muscle fiber, was detected in rare cases and was sporadic.

The data presented suggest that the appearance of spontaneous activity of muscle fibers in patients with myasthenia gravis is explained by the presence of advanced denervation changes caused by a disorder of neuromuscular transmission characteristic of myasthenia gravis. This is consistent with the fact of the absence of spontaneous activity in the vast majority of patients with reversible disorders of neuromuscular transmission, as well as with an increase in the degree of its severity in muscles in which, after administration of proserin, it was not possible to achieve complete restoration of the duration of the MUAP. Moreover, only 11% of such muscles had PF and only 3% - POV. In cases where the administration of proserin led to only partial compensation of the synaptic defect, PF and POF were recorded in a larger number of muscles.

Myasthenic syndromes

MYASTHENIC SYNDROME, SOMETIMES COMBINED WITH BRONCHOGENIC CARCINOMA (LAMBERT-EATON SYNDROME)

A detailed clinical and electrophysiological study of myasthenic syndrome, sometimes combined with small cell lung carcinoma, was carried out in 1956 by Lambert E. and Eaton L., and therefore it was called “Lambert-Eaton myasthenic syndrome” (MSLI).

The results they obtained were based on a study of 6 patients, 5 of whom were men: 2 patients had small cell carcinoma, 1 had pulmonary reticulosarcoma; one patient had cerebellar ataxia without signs of carcinomatous lesions. All patients had muscle weakness and fatigue, electrophysiological features, and a response to anticholinesterase drugs other than myasthenia gravis.

The ratio of men to women, according to most researchers, is 1.5:1. The age of patients with MSLI varies widely (14-80 years).

According to the literature, small cell carcinoma is detected in 90% of cases, although there are cases of combination with other types of lung tumors, kidney tumors, acute leukemia, reticulosarcoma, and even one observation concerns the combination of MSLI with malignant thymoma.

The time from the appearance of the first clinical signs of MSLI to the detection of a tumor is approximately 3 years.

It is important to emphasize the fact that the clinical manifestations of myasthenic syndrome and electrophysiological characteristics of neuromuscular transmission disorders in MSLI patients with and without bronchogenic carcinoma do not differ. According to most researchers, they do not differ in the characteristics of the immune response, in particular the titer of antibodies to voltage-gated calcium channels (VCC).

According to modern concepts, MSLI, with or without bronchogenic carcinoma, is an autoimmune disease, the pathogenesis of which is associated with the presence of autoantibodies to voltage-gated calcium channels (VCCs) of the presynaptic membrane of the neuromuscular junction.

An experimental study of the morphofunctional organization of the axon terminal membrane made it possible to identify four types of voltage-dependent calcium channels (P/Q, N, L and T), which differ in the speed of opening and the ability of various poisons to block these channels. In the blood serum of approximately 90% of MSLI patients, antibodies to voltage-gated calcium channels of the P/Q type are detected. However, a number of researchers have also discovered antibodies to N and L type channels.

In patients with MSLI, both with and without signs of a paraneoplastic process, in addition to specific autoantibodies, antibodies are also detected directed against various antigenic targets of the neuromuscular junction and others, for example, the gastric mucosa, tissue thyroid gland, Purkinje cells and other neuronal structures. Most researchers do not detect autoantibodies to acetylcholine receptors typical for myasthenia in patients with MSLI.

The literature describes a group of patients with a combination of myasthenia gravis and MSLI - overlap myasthenic syndrome, in which, at different periods of the course of the disease, they may predominate Clinical signs either myasthenia gravis or MSLI and, accordingly, antibodies to both AChR and PCC can be detected.

Symptoms of MSLI are:

Weakness and fatigue of the proximal legs and pelvic girdle, leading to a change in gait - “duck-like”. Weakness of the proximal parts of the arms is expressed to a much lesser extent.

Oculomotor disorders are detected very rarely and their severity is usually minimal. Swallowing and speech disorders are also rare.

Autonomic dysfunction nervous system with disorders of salivation and sweating, up to the development of “dry syndrome”, orthostatic hypotension, paresthesia, observed in approximately 65% ​​of patients, impotence.

Absence or significant suppression of deep reflexes.

Discrepancy between patient complaints of weakness and lack of real decline muscle strength in the tested muscles. This circumstance is associated with the peculiarities of neuromuscular transmission disorders, which is manifested by an increase in muscle strength during physical activity and a change in the reflex excitability of the affected muscle groups.

In 90% of MSLI patients, the effect of anticholinesterase drugs is questionable at best.

The use of drugs that facilitate the process of mediator release from the axon terminal, such as guanidine, 3-4-diaminopyridines, 4-aminopyridines, neuromidine (ipidacrine), as well as intravenous calcium, has a significantly greater effect than taking anticholinesterase drugs

One of the most important criteria for the diagnosis and differential diagnosis of MSLI is an electromyographic study of the state of neuromuscular transmission using the method of indirect supramaximal muscle stimulation.

A study of different groups of MSLI patients by gender, age, presence or absence of bronchogenic carcinoma showed that the main characteristics of the neuromuscular transmission block are:

Low amplitude of the M-response (negative phase less than 5.0 mV);

Increase - increment in the amplitude of subsequent M-responses in a series with high-frequency stimulation (20-50 pulses/s) more than 200%;

Increment of the M-response amplitude in response to the second of a pair of stimuli with an interpulse interval (IP) from 50 to 20 ms;

Significant - more than 200% - value of post-tetanic relief.

Congenital myasthenic syndromes (KMC) is a group of hereditary neuromuscular diseases caused by mutations of genes responsible for the formation and functional state of acetylcholine receptors, ion channels and enzymes that ensure the reliability of excitation from nerve to muscle.

Of 276 patients with KMC observed at the Mayo Clinic between 1988 and 2007, a presynaptic defect was identified in 20 patients, a synaptic defect in 37, and a postsynaptic defect in 219.

KMS classification:

Presynaptic defects (7%):

Myasthenic syndrome with choline acetyltransferase deficiency;

Myasthenic syndrome with a decrease in synaptic vesicles and quantum release of the transmitter;

Lambert-Eaton-like syndrome.

- nunidentified defects

Synaptic defects (13%):

Myasthenic syndrome with acetylcholinesterase deficiency.

Postsynaptic defects (80%):

Primary kinetic pathology with or without ACh receptor deficiency:

Slow channel syndrome;

Fast channel syndrome.

Primary ACh receptor deficiency with minor kinetic defect:

Myasthenic syndrome with rapsyn deficiency;

Dok 7-myasthenia gravis;

Myasthenic syndrome associated with Na-channel pathology;

Myasthenic syndrome with plectin deficiency.

Genetic analysis of acetylcholine receptor (AChR) subunits in patients with KMC has revealed numerous mutations associated with these diseases. Most KMC are postsynaptic, and their molecular genetic defect is based on mutations in the genes of various subunits of acetylcholine receptors (a, b, d, e). In some cases, this is manifested by kinetic anomalies of the receptors themselves, leading to disruption of their interaction with the mediator, in others - due to a predominant AChR deficiency associated with their death.

Primary sequence determination and mutational analysis of the collagen chain of the human endplate acetylcholinesterase subunit has revealed the molecular basis of acetylcholinesterase deficiency syndrome. In addition, electrophysiological studies using microelectrode technology (patch clamping) of the end plate of human muscles can determine individual channel currents passing through normal or mutated AChR channels.

Accurate diagnosis various types KMC is very important for rational therapy.

Typically, the diagnosis of KMC is based on a clinical history of fatigable weakness in the ocular, bulbar, and trunk muscles beginning in infancy or early childhood, family history (similarly affected relatives), decrement in M-response parameters on EMG examination, and a negative antibody test. to acetylcholine receptors. However, some forms of KMC nonetheless experience a later onset of the disease. Slow-channel syndrome - onset at any age, familial limb-girdle Dok 7-myasthenia gravis - typical onset at 5 years, possible onset from 13 to 19 years. In childhood myasthenia gravis associated with choline acetyltransferase deficiency, all symptoms can be episodic with severe respiratory crises due to fever, excitement or for no apparent reason and a complete absence of symptoms in the interictal period. The absence of a family history does not exclude an autosomal recessive mode of inheritance, a defective perinatal autosomal dominant gene in one of the parents, or a new mutation. Disorders of neuromuscular transmission do not occur in all muscles or all the time, and the distribution of muscle weakness is limited.

There are certain clinical signs that help differentiate different syndromes.

Thus, in patients with severe involvement of the trunk (truncal) or axial muscles, as in AChE deficiency, dysraphic features quickly develop with the formation of postural scoliosis and changes in one foot relative to the other in an upright position. Selective weakness of the muscles of the neck, forearm and finger extensors is typical of Slow-channel syndrome and in elderly patients with cholinesterase deficiency. A decrease in the reaction of the pupils to light is observed with cholinesterase deficiency. Involvement of the ocular muscles may be absent or slightly expressed in cholinesterase deficiency, Slow-channel syndrome, Dok 7-family limb-girdle myasthenia. Tendon reflexes are usually normal but reduced in about one in five patients with cholinesterase deficiency and in severe weakness in patients with a mutation affecting the AChR e subunit.

A pharmacological test with the administration of anticholinesterase drugs also provides significant assistance in diagnosing KMC. For example, patients with AChE enzyme deficiency and Slow-channel syndrome do not respond to AChE inhibitors, and the administration of drugs causes a deterioration in the patients' condition.

The diagnosis of KMC is usually confirmed by the presence of decrement during low-frequency indirect muscle stimulation (2-3 Hz) in one of the most affected muscles or increased jitter and blocking when studying single-fiber potentials. Decrement may be absent in myasthenic syndrome with choline acetyltransferase deficiency and between attacks in myasthenic syndrome with a decrease in synaptic vesicles and quantum release of the transmitter. In this syndrome, decrement can be induced by prolonged rhythmic stimulation with a frequency of 10 Hz or by physical exercise for several minutes before the testing series - stimulation with a frequency of 2 Hz.

In patients with AChE deficiency and Slow-channel syndrome, a single supramaximal stimulus evokes a repeated M response (SMAP). The interval between the first and subsequent potentials is 5-10 ms. Decrement upon stimulation with a frequency of 2-3 Hz is accompanied by a decrease in the second component more quickly than the main one. The test should be performed in patients not receiving AChE inhibitors, after a period of rest (rest) and with single nerve stimulation.

The amplitude of the first component of the M-response is usually normal, but the low-amplitude second component increases during physical stress or after injection of anticholinesterase drugs.

A positive test for antibodies to the acetylcholine receptor and to muscle-specific tyrosine kinase (MuSK) excludes congenital myasthenic syndrome. However, a negative test cannot unambiguously confirm KMC, given the presence of seronegative forms of myasthenia gravis. However, strong evidence of the absence of seronegative myasthenia gravis is the absence of immune deposits (IgG and complement) on the end plate.

Morphohistochemical study of muscle biopsies with KMC does not reveal pathology that allows us to differentiate these conditions from the results of studies of patients with autoimmune myasthenia. As a rule, type 2 muscle fiber atrophy is detected. In some cases, the predominance of the number of muscle types is type 1. These findings, however, are nonspecific, but may somehow answer the question of the presence of KMC.

In some cases, it is possible to reasonably assume the presence of a certain clinical form of KMC, but the assumption may be erroneous. Thus, a repeated M-response to a single supramaximal stimulus is observed only in two KMCs - congenital cholinesterase deficiency and Slow-channel syndrome. At the same time, similar changes in M-response parameters were observed in patients with autoimmune myasthenia gravis with the development or threat of development of a mixed crisis.

Refractoriness to taking anticholinesterase drugs and a slow reaction of the pupils to light indicate congenital endplate cholinesterase deficiency, however, similar symptoms are observed in patients with autoimmune myasthenia gravis during the development of a crisis.

Selective weakness of the neck, wrist, and extensor digitorum muscles is seen in Slow-channel syndrome and in older patients with endplate cholinesterase deficiency. A similar type of distribution of movement disorders is observed in patients with late onset myasthenia and myasthenia combined with thymoma, who have an undoubted autoimmune pathology.

In KMC, reminiscent of Lambert-Eaton syndrome, the first evoked M response is of low amplitude, but there is facilitation of more than 100% at high frequencies of stimulation, which does not allow it to be distinguished from an autoimmune syndrome associated with the presence of autoantibodies to voltage-gated calcium channels of the P/Q type .

KMC accompanied by episodes of apnea, with a history of repeated episodes of apnea, occurring either spontaneously or against the background of fever, vomiting, excitement or agitation. Moreover, between attacks of apnea, patients can either be completely healthy or have moderate myasthenic manifestations. Ptosis of the eyelids may or may not be present, but, as a rule, there are limitations in the mobility of the eyeballs. The decrement in the amplitude of the M-response may not be detected in a rested muscle, but it appears after several minutes of stimulation at a frequency of 10 impulses/s. These manifestations are characteristic of myasthenic syndrome with a decrease in synaptic vesicles and quantum release of the transmitter.

KMC associated with plectin deficiency and observed in patients with hereditary acquired bullous dermatitis and a form of muscular dystrophy. Deficiency of plectin (immunoreactivity) - a normal component that is present in skin hemidermosomes, in the sarcolemma, in the postsynaptic membrane and nuclear membrane of muscles - reduces the virulence of skin microorganisms (thinning or softening) and plectin is absent in the muscle.

With these and other KMC, the phenotype is uninformative and to determine the level of suffering (pre- or postsynaptic in nature), specialized electrophysiological and molecular genetic studies are necessary to determine the etiology and/or mutation underlying the disease.

To be effective, most codes require some level of stability. The work of Burns and others has established beyond all doubt that the activity of the central nervous system has this stability. Nerve tissue spontaneously generates electrical potentials. The brain, like the heart, pulses continuously. And, just as in heart, such pulsation is caused by slow potentials, and the occurrence of these latter depends on certain constants of the chemical environment in which the pulsating channel is located (Figure IV-5).

Figure IV-5. Cerebral Symphony (Verzeano et al, 1970).

A series of carefully conducted studies in the laboratory of Burns (1958) provided a comprehensive answer to a question that had long remained a fantasy: can the brain remain active even if it is completely isolated (neuronally) from another nerve tissue? The results of these experiments, as is often the case, did not fully support either the idea that brain activity is “spontaneous” or the idea of ​​the brain as a quiescent tabula rasa on which sensory experience is recorded. Berne discovered that even in an unanesthetized animal, an isolated strip of cortex remains inactive until electrical stimulation is applied to it for at least a short time; other data (Echlin et al., 1952; Gerard and Joung, 1937; Henry and Scoville, 1952; Ingvar, 1955; Libet and Gerard, 1939) indicate that spontaneous activity also exists in such preparations. In any case, even if one accepts Burns's cautious conclusion, a few strong electrical stimuli applied to the surface of the cortex produce a series of bursts of neural activity that typically continues for many minutes (or even hours) after the stimulation ceases.

Periodic waves of excitation can also be obtained in diffusely organized nervous tissue when it is electrically stimulated. They are similar to the excitation waves that occur in the non-anesthetized cerebral cortex in response to exposure to a few rare stimuli. Effects lasting many hours have been observed after brief stimulation of an intact sea anemone (Batham and Pantin, 1950). Recently, a luminescent response was described in marine “pansies” (a species of colored coral): after a series of stimulations, these colonies began to luminesce spontaneously, and not just in response to stimulation. To explain this phenomenon, one should turn to the mechanism of slow changes in the state of nervous tissue (an elementary form of memory associated with slow potentials?). These changes are caused by the influence of the environment and depend, of course, on the previous activity of the body. But they also have their own internal patterns and their own rhythm of activity, which causes repeated changes in the states of the nervous tissue, which makes them at each moment only partially dependent on environmental influences.

In short, it is generally accepted that groups of neurons of the type found in the cerebral cortex are in a state of rest in the absence of continuous sensory input. However, these groups of neurons can easily become excited and exhibit long-term activity. This means that we can assume that during “rest” they are in a state below the threshold of continuous self-excitation. The intact mammal has a mechanism that maintains central nervous system arousal above this resting level. This mechanism is the spontaneous discharge of receptors.

R. Granit (1955) spoke in detail about how he “was captured by the idea that spontaneous activity is integral part operation of sensory systems." He traced the history of this issue from the early observations of Lord E. Adrian and I. Zotterman (1926), E. Adrian and B. Matthews (1927a, b), performed on muscles and preparations of the optic nerve, to his own versatile experimental research. Moreover, his data support the assumption that this “spontaneous” activity of the senses makes them one of the most important “energizers,” or activators, of the brain. Now we can add to this that, probably, this spontaneous activity is the basis, the level at which and in relation to which neural coding occurs. Berne also presented data supporting this assumption (1968). Using microelectrodes, he discovered that approximately 1/3 large number The brain cells he examined during the entire time he was recording from them showed the stability of the average frequency of their discharges. These neurons responded to stimulation either by increasing the frequency of discharges or by inhibiting them. Each time, this was followed by a period during which the activity of the neuron changed reciprocally to the response. As a result, compensation occurred for changes in the average frequency of neuron discharges caused by stimulation. Thus, these cells create a powerful stable base on which the main characteristic of encoding and recoding depends: spatial structures of excitation can arise due to an increase in spontaneous activity in one place and its simultaneous inhibition in another.

Changes in total electromyograms in diseases of the peripheral neuromotor apparatus depend on changes in the PD of motor units and the nature of their involvement in the process of voluntary maximum effort. In all forms of diseases accompanied by a decrease in the duration of the AP MU (types I and II of changes in the structure of the AP MU), at maximum isometric muscle tension, an interference electromyogram is observed, which differs from the normal one by a decrease in the amplitude of the AP, but is significantly more saturated.

This is due to the fact that the strength of each MU, having lost part of the muscle fibers, is reduced and a higher frequency of operation of each motor unit is required to perform a motor act of the same force. In the presence of a smaller number of MUs, especially of increased duration (types IV and V of changes in the structure of MU APs), a reduced total electromyogram of the palisade type is observed, reflecting the synchronous activation of a small number of surviving MUs.

Spontaneous activity- PD recorded in the muscle using needle electrodes in the absence of voluntary activity or artificial stimulation of the muscle, including activity caused by the introduction of electrodes.

To forms of spontaneous activity that have diagnostic value include fibrillation potentials (PFs), positive sharp waves (PSWs) and fasciculation potentials.

PF- this is the PD of one, or in rare cases, several muscle fibers. Usually detected in the form of repeated discharges with a frequency of 0.1 to 150 per second. PF duration is up to 5 ms, amplitude is up to 500 μV.

POV- slow fluctuations of the potential of a characteristic shape - a rapid positive deviation of the potential, followed by a slow return of the potential to the negative side, which may end in a long negative phase of low amplitude. The duration of SEP varies from 2 to 100 ms, their amplitude is also different - from 20 to 4000 μV. POW is usually recorded in the form of discharges with a frequency of 0.1 to 200 per second.

To forms spontaneous The activity of muscle fibers that have diagnostic value should include myotonic and pseudomyotonic discharges. Myotonic discharge is a high-frequency discharge of biphasic (positive-negative) AP or POV, caused by voluntary movement or movement of the needle.

Amplitude and the frequency of the discharge increases and decreases, which is reflected in the appearance of the characteristic sound of a dive bomber when listening to the discharge. Pseudomyotonic discharges are similar high-frequency discharges that are not accompanied by a change in AP amplitude and stop suddenly. The appearance of myotonic discharges is almost pathognomonic for myotonia.

Pseudomyotonic discharges are detected in polymyositis, some types of metabolic myopathy and in zones of reinnervation (V type of DE changes) in neuronal disorders.

By EMG method Using cutaneous electrodes, it is possible to identify a number of characteristic types of muscle electrogenesis disorders characteristic of central and peripheral lesions of the motor pathway, diseases of the extrapyramidal system, a number of neuromotor disorders in myasthenia gravis, myotonia, as well as in other muscle diseases.

On EMG a number of parameters are identified, mainly based on an assessment of the amplitude of oscillations, their frequency and some time characteristics. For quantitative analysis of electromyograms, various methods of visual and instrumental characterization of pathological changes are used.